Field effect transistors based on organic semiconductors (OFET) are of interest for a large number of electronic applications. In particular, low manufacturing costs, flexible or unbreakable substrates or the production of transistors and integrated circuits over large active areas are possible therewith. For example, organic field effect transistors are suitable as pixel control elements in active matrix screens or for the production of extremely economical integrated circuits, as used, for example, for the active marking and identification of products and goods.
Since complex circuits can be built up using organic field effect transistors, there are numerous potential applications. Thus, for example, the introduction of RF-ID (RF-ID: radio frequency identification) systems based on this technology is considered a potential replacement for the bar code, which is susceptible to faults and can be used only in direct optical contact with the scanner. Passive RF-ID systems obtain their energy from the incident alternating field. The possible distance between reader and transponder depends on the radiant power and the energy requirement of the transponder. Silicon-based transponders therefore operate at supply voltages of about 3 V. Products which contain a silicon-based chip are too expensive for many applications. For example, a silicon-based identification tag is not suitable for the marking of foods (price, expiry date, etc.).
Organic field effect transistors usually consist of at least four different layers applied one on top of the other: a gate electrode, a dielectric, a source-drain contact layer and an organic semiconductor. The sequence of the layers may vary. To ensure the functionality, the individual layers must be structured, which is relatively complicated.
Polymers or organic semiconductors offer the potential of being able to use cheap printing techniques for their structuring and application. The gate potential for controlling the organic field effect transistors can be chosen to be all the lower but thinner in the form in which the gate dielectric (i.e. a dielectric layer) can be produced.
In polymer electronics, the thickness of the gate dielectric is generally optimized so that the solution of a polymer is spun out or printed on increasingly thinly (top-down). However, this procedure encounters its limits when it is intended to achieve layer thicknesses of less than 50 nm.
It is known that layers for organic field effect transistors can be built up by means of self-assembled layers comprising molecular monolayers (SEM: self-assembled monolayers).
In the articles by J. Collet, D. Vuillaume; “Nano-field effect transistor with an organic self-assembled monolayer as gate insulator”, Applied Physics Letters 73 (1998) 2681; J. Collet, S. Lenfant, D. Vuillaume, O. Bouloussa, F. Rondelez, J. M. Gay, K. Kham, C. Chevrot; “High anisotropic conductivity in organic insulator/semiconductor monolayer heterostructure”, Applied Physic Letters 76 (2000) 1339, and J. Collet, O. Tharaud, A. Chapoton, D. Vuillaume; “Low-voltage, 30 nm channel length, organic transistors with a self-assembled monolayer as gate insulating films”, Applied Physics Letters 76 (2000) 1941, which describes such layers.
These layers are also discussed in the articles by Pradyt Ghosh, Richard M. Crooks; “Covalent Grafting of a Pattered”, Hyperbranched Polymer onto Plastic Substrate Using Microcontact Printing”, J. Am. Chem. Soc. 121 (1999) 8395-8306, and William M. Lackowski, Pradyut Ghosh, Richard M. Crooks; “Micron-Scale Patterning of Hyperbranched Polymer Films by Micro-Contact Printing;”, J. Am. Chem. Soc. 121 (1999) 1419-1420 and Jacob Sagiv; “Process for the production of built-up films by the stepwise adsorption of individual monolayers”, and U.S. Pat. No. 4,539,061 (1985).
The articles by Collet et al. describe materials that make it possible to use transistors having SAM layers. Vinyl-terminated silanes have anchor groups on hydroxyl-containing substrate surfaces to form an SAM. This is subsequently chemically aftertreated in order to bind further molecules chemically to the SAM (cf. article by Sagiv et al.), or surfaces which permit further processing are produced (cf. article by Collet, Tharaud et al.).
It is disadvantageous that these layers do not form a dense dielectric layer without aftertreatment. The chemical aftertreatments used converts only 70 to 90% of the terminal groups in a reaction time of 48 to 120 hours. This chemical aftertreatment takes too long for the production of large quantities.
In principle, it is also possible to bind polymers via a plurality of coordination sites to a surface (Self-Assembled Polymers). This is disclosed in U.S. Pat. No. 5,728,431, U.S. Pat. No. 5,783,648 (1998) and U.S. Pat. No. 5,686,549.